U.S. patent application number 17/288052 was filed with the patent office on 2021-12-09 for inkjet printing process.
The applicant listed for this patent is LUXEMBOURG INSTITUTE OF SCIENCE AND TECHNOLOGY (LIST). Invention is credited to Emmanuel DEFAY, Sebastjan GLINSEK, Nicolas GODARD, Daniele SETTE.
Application Number | 20210379898 17/288052 |
Document ID | / |
Family ID | 1000005823271 |
Filed Date | 2021-12-09 |
United States Patent
Application |
20210379898 |
Kind Code |
A1 |
GODARD; Nicolas ; et
al. |
December 9, 2021 |
INKJET PRINTING PROCESS
Abstract
An only inkjet-printing-based process for depositing functional
materials, in various instances PZT, Bi-based material or
(K,Na)-based material, on a substrate, in various instances
platinized silicon. Substrate templating (via SAMs) and material
deposition are both performed by an inkjet printing process.
Additionally, a composition to be used as a SAM precursor ink which
is a thiol in a solvent mixture. Further, a cartridge for a
printing machine with such a composition. Still further, the use of
such a cartridge, alone, or as a kit with another cartridge
containing a precursor of the functional material, in particular to
perform both steps of the printing method. Finally, a product, for
instance a microsystem, obtained by the process.
Inventors: |
GODARD; Nicolas; (Musson,
BE) ; SETTE; Daniele; (Grenoble, FR) ;
GLINSEK; Sebastjan; (Dudelange, LU) ; DEFAY;
Emmanuel; (Esch-sur-Alzette, LU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LUXEMBOURG INSTITUTE OF SCIENCE AND TECHNOLOGY (LIST) |
Esch-sur-Alzette |
|
LU |
|
|
Family ID: |
1000005823271 |
Appl. No.: |
17/288052 |
Filed: |
October 24, 2019 |
PCT Filed: |
October 24, 2019 |
PCT NO: |
PCT/EP19/79049 |
371 Date: |
April 23, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B81C 1/00373 20130101;
B41J 2/17503 20130101; B81C 2201/0185 20130101; C09D 11/36
20130101 |
International
Class: |
B41J 2/175 20060101
B41J002/175; C09D 11/36 20060101 C09D011/36 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2018 |
LU |
LU100971 |
Claims
1.-16. (canceled)
17. An inkjet printing process on a substrate comprising (a) a step
of deposition of a self-assembled monolayer (SAM) on the substrate;
(b) a step of printing of a material within the boundaries of the
SAM, the material being a composition containing at least one of
the following: at least one of PZT doped with either Fe, K, Nb, Ta,
and Nd; BiFeO.sub.3 or (Bi,Re)FeO.sub.3, where Re is rare-earth
metal comprising at least one of La, Nd, Sm, Eu, etc.;
(Bi.sub.0.5Na.sub.0.5)TiO.sub.3 or (Bi.sub.0.5K.sub.0.5)TiO.sub.3
and their solid solutions as well as their solid solutions with
BaTiO.sub.3; (K,Na)NbO.sub.3 or (K,Na,Li)(Sb,Ta,Nb)O.sub.3 and
their solid solutions with (Bi.sub.0.5Na.sub.0.5)TiO.sub.3 and
BaTiO.sub.3; at least one of Al.sub.2O.sub.3, SiO.sub.2, TiO.sub.2,
ZrO.sub.2, ZnO, or ZnO, doped with Al; at least one of solid
solutions of HfO.sub.2--ZrO.sub.2, CrO.sub.2, VO.sub.2, CuO,
Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, IrO.sub.2, BaO, SrO, MgO,
Y.sub.2O.sub.3, CeO.sub.2, Cs.sub.2O, WO.sub.3, MoO.sub.3, or
RuO.sub.2; HfO.sub.2 doped with at least one of Y, Si, Sr, La, Gd,
and Al; at least one of In.sub.2O.sub.3 or SnO.sub.2 or any solid
solution between In.sub.2O.sub.3 and SnO.sub.2; and at least one of
LaNiO.sub.3 or SrRuO.sub.3, wherein both steps (a) and (b) are made
by inkjet printing.
18. The printing process according to claim 17, wherein the SAM ink
is a composition made of a thiol in a solvent mixture of alcohols
and ethers, and the substrate is made of a high surface energy
material containing at least a noble metal.
19. The printing process according to claim 18, wherein the solvent
mixture of the SAM ink is made of 60 to 90 vol % of
2-methoxyethanol.
20. The printing process according to claim 18 wherein the thiol is
1-dodecanethiol in a quantity of 0.01 to 0.0001 M.
21. The printing process according to claim 17 wherein said
material is diluted to 0.2 M with a solvent made of 65 (.+-.5) vol
% 2-methoxyethanol, 25 (.+-.5) vol % glycerol and 10 (.+-.5) vol %
ethylene glycol.
22. The printing process according to claim 17 wherein the process
further comprises at least one of the following steps: (c) drying;
(d) pyrolysis; and (e) crystallization.
23. The printing process according to claim 22, wherein the steps
(a) to (d) are carried out in that order and are repeated one time
or more, defining a cycle, and step (e) is performed after step (d)
every n cycle, n being equal or greater than 1, such that a
multi-layer functional material is printed on the substrate.
24. The printing process according to claim 17, wherein at least
one of the SAM and the material have the following rheological
properties: a viscosity within the range 1-15 mPas and a surface
tension within the range 20-40 mN/m.
25. A composition made of 1-dodecanethiol in a solvent mixture of
2-methoxyethanol and glycerol.
26. The composition according to claim 25, wherein the solvent
mixture consists of 60 to 90 vol % of 2-methoxyethanol, the
complement being glycerol.
27. The composition according to claim 25, wherein the
1-dodecanethiol is in a quantity of 0.01 to 0.0001 M.
28. A kit, said kit comprising: at least one cartridge for a
printing machine containing a composition made of 1-dodecanethiol
in a solvent mixture of 2-methoxyethanol and glycerol; and at least
one cartridge comprising a composition containing at least one of
the following: at least one of PZT doped with either Fe, K, Nb, Ta,
and Nd; BiFeO.sub.3 or (Bi,Re)FeO.sub.3, where Re is rare-earth
metal comprising at least one of La, Nd, Sm, Eu, etc.;
(Bi.sub.0.5Na.sub.0.5)TiO.sub.3 or (Bi.sub.0.5K.sub.0.5)TiO.sub.3
and their solid solutions as well as their solid solutions with
BaTiO.sub.3; (K,Na)NbO.sub.3 or (K,Na,Li)(Sb,Ta,Nb)O.sub.3 and
their solid solutions with (Bi.sub.0.5Na.sub.0.5)TiO.sub.3 and
BaTiO.sub.3; at least one of A12O.sub.3, SiO.sub.2, TiO.sub.2,
ZrO.sub.2, ZnO, or ZnO, doped with Al; at least one of solid
solutions of HfO.sub.2--ZrO.sub.2, CrO.sub.2, VO.sub.2, CuO,
Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, IrO.sub.2, BaO, SrO, MgO,
Y.sub.2O.sub.3, CeO.sub.2, Cs.sub.2O, WO.sub.3, MoO.sub.3, or
RuO.sub.2; HfO.sub.2 doped with at least one of Y, Si, Sr, La, Gd,
and Al; at least one of In.sub.2O.sub.3 or SnO.sub.2 or any solid
solution between In.sub.2O.sub.3 and SnO.sub.2; and at least one of
LaNiO.sub.3 or SrRuO.sub.3.
29. The printing process according to claim 17 further comprising
preforming the process using a cartridge for a printing machine
containing a composition made of 1-dodecanethiol in a solvent
mixture of 2-methoxyethanol and glycerol.
30. The printing process according to claim 18, wherein the thiol
is 1-dodecanethiol, the solvent mixture of alcohols and ethers is
2-methoxyethanol and glycerol, and the noble metal of the substrate
is taken from the group: Pt, Au, Cu, Ir, Pd, Ru.
31. The printing process according to claim 18 wherein the thiol is
1-dodecanethiol in a quantity of 0.001 M in the solvent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present invention is the US national stage under 35
U.S.C. .sctn. 371 of International Application No.
PCT/EP2019/079049 which was filed on Oct. 24, 2019, and which
claims the priority of application LU 100971 filed on Oct. 25,
2018, the content of which (text, drawings and claims) are
incorporated here by reference in its entirety.
FIELD
[0002] The invention deals with the field of inkjet printing of
functional materials on substrates. The invention, in various
instances, is aimed at printing microsystems, the substrate being
at least partially made of platinized silicon.
BACKGROUND
[0003] Printing functional materials, in particular functional
oxides, on high surface energy materials presents particular
difficulties since the ink tends to spread away on the material
surface instead of sticking to the precise point where the droplet
of ink has been deposited.
[0004] To counter-act the spreading of the ink, the surface to be
printed is first prepared by deposition of a barrier and then the
printed material is applied such that it does only spread within
the boundaries of the barrier.
[0005] This first step of barrier deposition is commonly described
as "templating", since it consists in the realization of a template
on the substrate.
[0006] Literature proposes two main solutions to limit the
spreading of the ink, i.e., hard templates which are physical
barriers such as lithographically patterned molds, or soft
templates which are chemical barriers such as self-assembled
monolayers (SAMs). The present invention focuses on soft
templates.
[0007] The deposition of soft templates is known to be achieved by
photolithography such as described in document U.S. Pat. No.
8,888,253 B2. A whole surface is covered by SAMs and the area to be
printed is cleaned from SAMs by a photolithography process. An
alternative technology can be micro-contact printing (see H. Lee et
al., MTL Ann. Res. Rep., MS15, 2009), wherein a
polydimethylsiloxane stamp impregnated with a fluorinated thiol
solution is pressed against the substrate.
[0008] Alkanethiol self-assembled monolayers (SAMs) can bond to
noble metals such as gold, platinum, copper, palladium, iridium and
ruthenium. The surface-exposed hydrocarbon chain reduces surface
energy and the surface becomes `hydrophobic` or `ink-phobic`
(ink-repelling).
[0009] After the step of deposition of SAMs, the step of printing
with the desired functional material is carried out. This is
usually done by inkjet printing.
[0010] As a consequence, the known techniques employ two
technologies, a first technology for the first step (deposition of
SAM) and a second technology (i.e., inkjet printing) for the second
step (deposition of ink).
[0011] Many drawbacks result from this need of two technologies.
For instance, the proper positioning of the substrate in the second
step which should match perfectly the first step is a difficulty.
Furthermore, it lacks practicability and is time, cost and
precursor consuming.
SUMMARY
[0012] The present invention aims at improving the known processes
of printing functional materials on high surface energy substrates
while overcoming the above-mentioned drawbacks.
[0013] The stated problem is solved by an only
inkjet-printing-based process. In other words, substrate templating
and material printing are both processed with the same technology.
This is made possible by the development of a SAM precursor ink
that is suitable for being printed by inkjet process. In this
context of printing of functional materials, known SAMs do not have
such properties.
[0014] This solution is cost and time efficient, and removes the
need to reposition the substrate after the step of templating. As a
consequence, the precision of the print is considerably
improved.
[0015] The stated problem is also solved by the composition of the
SAM precursor ink which is a 1-dodecanethiol in a solvent mixture
of 2-methoxyethanol and glycerol. In general, alkanethiols are
particularly suited for adhering to the substrate. The mixture with
glycerol makes the SAM precursor ink suitable for being printed by
inkjet. In particular, this solvent mixture impacts the viscosity
of the SAM precursor ink which must be such that it can be
contained in an inkjet cartridge and droplets of adequate size can
be formed and can adhere to the substrate. Indeed, glycerol is
known for its viscous properties, particularly relevant when
printing by jetting droplets. During the inkjet process, the SAM
precursor ink is also submitted to a temperature at which solvent
vapor pressure may be high. A solvent with a too low boiling point
would evaporate and would therefore not play its role. The
particular composition of the SAM precursor ink according to the
invention is made with a solvent with a higher boiling point that
makes it suitable for being inkjet-printed.
[0016] The problem is also solved by a cartridge for a printing
machine, the cartridge containing such a composition.
[0017] The invention also relates to the use of such a cartridge,
alone, or as a kit with another cartridge containing the functional
material, in particular to perform steps of the printing method of
the invention.
[0018] The invention also relates to the product obtained by the
process of the invention. As is explained below, the use of such an
only inkjet-printing-based process can be identified on the final
product, for instance a microsystem, which has been at least
partially manufactured by the printing process.
[0019] Printing Process
[0020] According to the invention, the printing process is as
prescribed in claim 1.
[0021] In an exemplary embodiment, the process comprises
furthermore at least one of the following steps:
[0022] (c) drying;
[0023] (d) pyrolysis;
[0024] (e) crystallization;
[0025] and, in various instances all these steps are performed in
that order, and after step (b).
[0026] These steps allow to get rid of the SAM material and to
synthesize the printed functional material. When all three steps
are carried out, an annealing process is achieved.
[0027] The steps of drying, pyrolysis and crystallization can be as
follows: drying at 130.degree. C. for 3 minutes, pyrolysis at
350.degree. C. for 8 minutes and crystallization at 700.degree. C.
for 5 minutes. An optional second step of drying at about
250.degree. C. for about 3 minutes can be applied. The temperatures
and the durations of each step depend on the nature of the
functional material and the thickness of the layer (i.e. density of
droplets printed). The skilled person would know to which extent
they can divert from these values while reaching the same effects.
Also, for a given functional material, the temperature and duration
can be (inversely) varied to obtain the same effects. For instance,
drying at ambient temperature is possible but this requires a
substantially longer duration than .sup.3 minutes.
[0028] In various instances, the thickness of a layer of functional
material is between 5 and 500 nm, preferably between 30 and 150 nm,
for example from 50 to 90 nm, e.g., about 70 nm. The thickness of
the layer is governed by the density of droplets printed in step
(b). Layers which are thinner than 5 nm would not be continuous,
since the droplets of functional material would spread
discontinuously on the substrate. Layers which are thicker than 500
nm tend to crack during the drying process.
[0029] In an exemplary embodiment, steps (a) to (d) are carried out
and are repeated one time or more, defining a cycle, and step (e)
is performed after step (d) every n cycle, n being equal or greater
than 1, preferably n=3 or n=4. Indeed, the crystallization step is
not essential for each cycle. This multi-cycle or multi-layer
process allows to print a thicker film of functional material.
[0030] The SAM may decompose or be degraded due to the annealing
process.
[0031] There is therefore a need to re-deposit SAM at the beginning
of each deposition of a new layer.
[0032] The volume of the droplets can be from 1 pL to 20 pL,
preferably 10 pL or 12 pL.
[0033] The density of deposition of the functional material can be
from 100 droplets/mm.sup.2 to 7000 droplets/mm.sup.2, in various
instances a few hundreds of droplets, for example 700.+-.50
droplets/mm.sup.2.
[0034] The density of deposition of the SAM is such that the
distance between two successive drops is less than 40% of the
diameter of the drop once it is deposited on the substrate. This
serves the purpose of preventing a "jagged edge effect" due to the
superimposition of adjacent droplets. Indeed, a small distance
between two successive droplets makes it possible to achieve a
continuous edge.
[0035] The droplets are deposited at a rate of a few thousands of
droplets per second, i.e. a rate from 1,000 to 200,000 droplets per
second, in various instances 1,000 to 20,000 droplets per second,
for example 1,000 drops per second.
[0036] The pattern of the template defined by the deposition of the
SAM can be of any desired shape, form or size. A square-grid
pattern is described in the present application as an exemplary
embodiment although any other shape, can be printed like a circle
or any random closed line. The order of magnitude of the template
can be from 10 .mu.m to a few cm. In that sense, the method of the
invention is particularly flexible.
[0037] In a particular exemplary embodiment of the printing method,
at least one of the steps of drying, pyrolysis or crystallization
is carried out within the printing machine. The handling of the
substrate between the printing of two successive layers is
therefore avoided. To this end, the machine is equipped with
heating means such as IR-heating means, laser, photonic annealing
or any conventionally known heating means. The structure of the
machine is such that it is suitable for resisting to such
temperatures. A thermal shield to isolate the substrate or a
removable oven can be provided. During these steps, the printing
head with the ink is in various instances put at a distance from
the substrate being heated, to prevent any risk of deterioration to
the ink.
[0038] In another exemplary embodiment, the printing method does
not make use of cartridges. The printing machine comprises a
plurality of tanks, each containing one of the "raw" compositions:
alkanethiol, glycol ether, ethylene glycol, glycerol and functional
material. The raw compositions are fed to two mixing chambers at
desired proportions to obtain the composition of the SAM precursor
ink in one chamber and the composition of functional material ink
in another chamber. These two (final) compositions are then fed to
the printing head. This simplifies the re-filling of the machine by
avoiding the need of frequent cartridge replacement. With such an
arrangement, the machine can keep on printing and does not need to
be stopped when an empty cartridge is to be replaced.
[0039] Composition of the SAM Precursor Ink
[0040] The composition used as SAM precursor ink is a thiol, in
various instances an alkanethiol, for example 1-dodecanethiol, in a
solvent mixture of alcohols and ethers, in various instances
glycols, glycol ethers, polyols, polyol ethers, for example,
2-methoxyethanol and glycerol, and the substrate is made of high
surface energy material containing at least a noble metal, in
various instances a metal of the group Pt, Au, Cu, Ir, Pd, Ru.
[0041] In an exemplary embodiment, the composition is made of an
alkanethiol in a solvent mixture of 2-methoxyethanol and
glycerol.
[0042] The following rheological properties are important for the
solvent to be "inkjetable": a viscosity within the range: 1-15 mPas
and a surface tension within the range: 20-40 mN/m. Typical solvent
mixture consist of 2-methoxyethanol and glycerol. Advantageously,
the proportions of the mixture are from 60 to 90 vol % of
2-methoxyethanol, in various instances from 70 to 80 vol %, for
example about 75 vol %, the complement being glycerol. These
proportions give the best results in terms of aptitude to be
inkjet-printed.
[0043] In an exemplary embodiment, the alkanethiol is
1-dodecanethiol CH.sub.3(CH.sub.2).sub.11SH, in various instances
in a quantity of 0.1 to 0.00001 M in the solvent, in various
instances 0.01 to 0.0001 M, for example 0.001 M. 1-Dodecanethiol
has particularly good properties to adhere to high surface energy
metals.
[0044] Other similar solvents or alkanethiols (described by the
general formula RSH where R is C.sub.nH.sub.2n+1) can be used.
[0045] Composition of the Functional Material
[0046] Concerning the material to be deposited on the substrate,
various embodiments of the invention concerns PZT ink
(Pb(Zr,Ti)O.sub.3) or PZT doped with Fe, K, Nb, Ta, and/or Nd. The
PZT ink consists of a standard chemical solution deposition (CSD or
sol-gel) material modified with solvents.
[0047] A specific embodiment of the PZT ink can be a PZT ink that
has a near-morphotropic-phase-boundary composition (MPB). A mixture
of dehydrated lead(II) acetate, zirconium(IV) butoxide and
titanium(IV) isopropoxide in 2-methoxyethanol with 10% excess lead
is heated at reflux during two hours to ensure homogenization and
stabilization of alkoxide species via ligand exchange. The
resulting PZT solution is then diluted to 0.2 M with ethylene
glycol and glycerol to adjust ink viscosity and surface tension for
efficient droplet ejection using cartridges commercially available
such as Dimatix.RTM..
[0048] The ink should in various instances have the following
rheological properties: a viscosity within the range: 1-15 mPas and
a surface tension within the range: 20-40 mN/m. In an exemplary
embodiment, the PZT ink is diluted in 65 (.+-.5) vol %
2-methoxyethanol, 25 (.+-.5) vol % glycerol and 10 (.+-.5) vol %
ethylene glycol.
[0049] Alternatively, the functional material can be PLZT
((Pb,La)(Zr,Ti)O.sub.3), PbTiO.sub.3, PbZrO.sub.3,
Pb(Mg,Nb,Ti)O.sub.3, BaTiO.sub.3, (Ba,Ca)(Ti,Zr)O.sub.3 or any
equivalent.
[0050] Alternatively, the functional material can be BiFeO.sub.3 or
(Bi,Re)FeO.sub.3, where Re is rare-earth metal, such as La, Nd, Sm,
Eu, etc.
[0051] The functional material can also be
(Bi.sub.0.5Na.sub.0.5)TiO.sub.3 or (Bi.sub.0.5K.sub.0.5)TiO.sub.3
or their solid solutions as well as their solid solutions with
BaTiO.sub.3.
[0052] The functional material can be (K,Na)NbO.sub.3,
(K,Na,Li)(Sb,Ta,Nb)O.sub.3 or their solid solutions with
(Bi.sub.0.5Na.sub.0.5)TiO.sub.3 and BaTiO.sub.3.
[0053] The functional material can be selected from the group:
(K,Na)NbO.sub.3, (K,Na,Li)(Sb,Ta,Nb)O.sub.3 and their solid
solutions with (Bi.sub.0.5Na.sub.0.5)TiO.sub.3 and BaTiO.sub.3.
[0054] The functional material can be any of Al.sub.2O.sub.3,
SiO.sub.2, TiO.sub.2, ZrO.sub.2, ZnO, or ZnO, doped with Al.
[0055] The functional material can be any of the solid solutions of
HfO.sub.2--ZrO.sub.2, CrO.sub.2, VO.sub.2, CuO, Fe.sub.2O.sub.3,
Fe.sub.3O.sub.4, IrO.sub.2, BaO, SrO, MgO, Y.sub.2O.sub.3,
CeO.sub.2, Cs.sub.2O, WO.sub.3, MoO.sub.3, or RuO.sub.2.
[0056] The functional material can be HfO.sub.2 doped with: Y, Si,
Sr, La, Gd, and/or Al.
[0057] The functional material can be In.sub.2O.sub.3 or SnO.sub.2
and solid solution between the two.
[0058] Finally, the functional material can be LaNiO3 or
SrRuO3.
[0059] These various embodiments of the material share common
rheological properties which give them the aptitude to be ink
printed.
[0060] Substrate
[0061] As for the material of the substrate, the invention aims at
printing on any material with high surface energy containing at
least a metal and compatible with the formation of SAMs such as
materials comprising Pt, Au, Cu, Ir, Pd, Ru or any material with
similar properties. This material can be deposited on silicon,
glass, steel or polymer. The most preferable material for the
substrate to be printed by the disclosed invention is platinized
silicon.
[0062] Platinum has very high surface energy (.about.1 J m.sup.-2).
Due to extreme wetting, the direct deposition of functional
materials by inkjet printing of organic solvent-based inks is
inadequate. Other noble metals can present similar properties.
[0063] Cartridges
[0064] The invention also relates to a printing cartridge
containing the templating ink, i.e. the composition aimed at being
used as SAM precursor ink.
[0065] The invention also relates to a kit of at least one such
cartridge and at least one cartridge containing the functional
material.
[0066] The cartridges can have a capacity of 3 mL and the size of
the nozzle can be of 21 .mu.m. Other cartridges can be used
according to the machine used or the size or shape of the
pattern/print to be achieved.
[0067] The cartridge for the template ink and the cartridge for the
functional material ink can be identical. They can also be
different. Indeed, a bigger cartridge can be used for the
functional material, such that, for instance, the replacement of
the two cartridges can occur simultaneously.
[0068] The printing method of an exemplary embodiment of the
invention can make use of more than two cartridges. For instance,
there can be more than one cartridge of one particular material for
consumption reasons, to avoid any maintenance when depositing a
high volume of material.
[0069] Alternatively or complementarily, there can also be more
than two materials involved. For instance, when depositing several
layers, two successive layers of functional material or two
successive layers of SAM can be made of different materials. There
are therefore at least three cartridges comprising three different
compositions. The kit of the invention can include these at least
three cartridges.
[0070] This technique makes it possible to print superior layers of
electrodes. These printed top electrodes can be made of Ag, Cu, Pt
or ITO (indium tin oxide). All these materials are known to be
printable.
[0071] Product
[0072] The particular but not exhaustive applications of the
printing process of the invention are microsystems, passive
capacitors, silicon wafers or integrated piezoelectric devices. For
instance, the method of the invention can be used to print a series
of piezoelectric actuators spaced from each other of 50
microns.
[0073] The invention also relates to the final product resulting
from the printing process. Analyses have shown that the final
product can have similar electrical properties as a microsystem
obtained by the known methods. Secondary ion mass spectrometry
(SIMS) analysis shows however that a product directly obtained by
the method of the invention exhibits traces of sulfur in the
functional material film. The presence of sulfur was detected
across the whole thickness of a crystallized PZT film. A higher
concentration of sulfur was however found at the edge of the
printed PZT pattern. It could be ascribed to the diffusion of
thiols in the functional material film, due to the coexistence of
both inks in the liquid state after printing. The templating lines
contain a relatively large amount of residual solvent and
non-grafted thiols that can diffuse in the liquid film of
functional material. Thiols used for substrate templating are the
only possible source of sulfur since they are the only
sulfur-containing species used in the whole process.
[0074] As a consequence, by performing a SIMS analysis on a
product, one can identify whether a particular product has been
produced by the printing method of the invention.
DRAWINGS
[0075] FIG. 1 is an exemplary illustration of a cross section of a
substrate, in accordance with various embodiments of the
invention.
[0076] FIG. 2 is an exemplary diagram summarizing the preparation
of a functional material, in accordance with various embodiments of
the invention.
[0077] FIG. 3 illustrates an exemplary embodiment of the printing
method, in accordance with various embodiments of the
invention.
[0078] FIG. 4 illustrates exemplary top view pictures of the
printed pattern of films, in accordance with various embodiments of
the invention.
[0079] FIG. 5 exemplarily shows the thickness of the deposition, in
accordance with various embodiments of the invention.
[0080] FIG. 6 exemplarily shows the results of a SIMS analysis, in
accordance with various embodiments of the invention.
DETAILED DESCRIPTION
[0081] FIG. 1 shows a cross section (not to scale) of a substrate
that can be used for the printing process of the invention. The
substrate in various instances comprises a silicon base with a
platinum coating.
[0082] FIG. 2 details the process employed to obtain a functional
material. In this example, PZT ink is obtained after reflux and
dilution.
[0083] A mixture of dehydrated lead(II) acetate, zirconium(IV)
butoxide and titanium(IV) isopropoxide in 2-methoxyethanol with 10%
excess lead is heated at reflux during two hours to ensure
homogenization and stabilization of alkoxide species via ligand
exchange. The resulting PZT sol is then diluted to 0.2 M with
ethylene glycol and glycerol to adjust ink viscosity and surface
tension for efficient droplet ejection. For instance, the PZT can
be diluted in 65 vol % 2-methoxyethanol, 25 vol % glycerol and 10
vol % ethylene glycol.
[0084] Other equivalent processes can be used to obtain the various
compositions of ink discussed above.
[0085] FIG. 3 shows an example of pattern/template and a particular
printing process according to an embodiment of the invention. A
grid-like pattern is printed with SAMs (step (a) of the printing
process). In practice, a first series of parallel lines is printed
and then a second series of parallel lines perpendicular to the
first series is printed. Then the functional material is printed
within the boundaries of the grid-like pattern (step (b) of the
printing process).
[0086] In a particular example, the steps of drying, pyrolysis and
crystallization are applied to obtain a final (dry) film on the
substrate, as illustrated on the right side of FIG. 3.
[0087] In a particular example of a product obtained by the
invention, the two-step full-inkjet-printing process has been used
to fabricate an array of 500.times.500 .mu.m.sup.2 PZT squares. The
obtained 80 nm-thick structures are crystallized in perovskite
phase.
[0088] FIG. 4 shows pictures taken with an optical microscope of
the films that can be obtained after multi-layer printing process.
The printing steps of FIG. 3 are repeated. They are carried out in
the same area of the substrate to build one layer at a time. This
means that a precise repositioning of the printing head relative to
the substrate for each new layer is performed.
[0089] FIG. 5 shows the thickness profile of one of the squares.
The measurement of the thickness was made after crystallization of
each of the successive layers and prior to printing the next layer.
We can see regular thickness along the transverse direction of the
square. We can also see that the method of the invention allows a
precise positioning of the layers one onto each other. Of course,
by varying the density of droplets from one layer to another layer,
or varying the functional material, a wide variety of heterogenous
products can be printed.
[0090] FIG. 6 shows the results of the SIMS analysis (imaging mode)
of a film realized with the printing method of the invention. An
elemental mapping of titanium, oxygen and sulfur was performed in
the edge area of a printed PZT square. Sulfur was mostly detected
at the edge of the PZT square.
[0091] Both the functional material and the SAM precursor inks were
liquid and were in contact with each other during the printing
process. The sulfur detected in the layer of functional material
can only originate from thiols that have diffused into the
functional material precursor ink while both were in liquid state.
Such diffused sulfur is not observed when SAMs are deposited by any
other method because in these known methods, the liquid functional
material ink is only printed once the SAM is formed and there is no
residual liquid on the substrate.
[0092] Although the printing process, the composition of the SAM,
the composition of the functional material, the substrate material
and the cartridges have been described in details in separate
paragraphs of the description, it has to be noted that each
particular embodiment of one of these elements is combinable with
each particular embodiment of another one of these elements.
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